69 lines
3.1 KiB
Markdown
69 lines
3.1 KiB
Markdown
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---
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id: 587d8256367417b2b2512c77
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title: Adjacency List
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challengeType: 1
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---
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## Description
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<section id='description'>
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Graphs can be represented in different ways. Here we describe one way, which is called an <dfn>adjacency list</dfn>.
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An adjacency list is essentially a bulleted list where the left side is the node and the right side lists all the other nodes it's connected to. Below is a representation of an adjacency list.
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<blockquote>Node1: Node2, Node3<br>Node2: Node1<br>Node3: Node1</blockquote>
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Above is an undirected graph because <code>Node1</code> is connected to <code>Node2</code> and <code>Node3</code>, and that information is consistent with the connections <code>Node2</code> and <code>Node3</code> show. An adjacency list for a directed graph would mean each row of the list shows direction. If the above was directed, then <code>Node2: Node1</code> would mean there the directed edge is pointing from <code>Node2</code> towards <code>Node1</code>.
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We can represent the undirected graph above as an adjacency list by putting it within a JavaScript object.
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<blockquote>var undirectedG = {<br> Node1: ["Node2", "Node3"],<br> Node2: ["Node1"],<br> Node3: ["Node1"]<br>};</blockquote>
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This can also be more simply represented as an array where the nodes just have numbers rather than string labels.
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<blockquote>var undirectedGArr = [<br> [1, 2], # Node1<br> [0], # Node2<br> [0] # Node3<br>];</blockquote>
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</section>
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## Instructions
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<section id='instructions'>
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Create a social network as an undirected graph with 4 nodes/people named <code>James</code>, <code>Jill</code>, <code>Jenny</code>, and <code>Jeff</code>. There are edges/relationships between James and Jeff, Jill and Jenny, and Jeff and Jenny.
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</section>
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## Tests
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<section id='tests'>
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```yml
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- text: <code>undirectedAdjList</code> should only contain four nodes.
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testString: 'assert(Object.keys(undirectedAdjList).length === 4, "<code>undirectedAdjList</code> should only contain four nodes.");'
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- text: There should be an edge between <code>Jeff</code> and <code>James</code>.
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testString: 'assert(undirectedAdjList.James.indexOf("Jeff") !== -1 && undirectedAdjList.Jeff.indexOf("James") !== -1, "There should be an edge between <code>Jeff</code> and <code>James</code>.");'
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- text: There should be an edge between <code>Jill</code> and <code>Jenny</code>.
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testString: 'assert(undirectedAdjList.Jill.indexOf("Jenny") !== -1 && undirectedAdjList.Jill.indexOf("Jenny") !== -1, "There should be an edge between <code>Jill</code> and <code>Jenny</code>.");'
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- text: There should be an edge between <code>Jeff</code> and <code>Jenny</code>.
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testString: 'assert(undirectedAdjList.Jeff.indexOf("Jenny") !== -1 && undirectedAdjList.Jenny.indexOf("Jeff") !== -1, "There should be an edge between <code>Jeff</code> and <code>Jenny</code>.");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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var undirectedAdjList = {
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};
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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var undirectedAdjList = {
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"James": ["Jeff"],"Jill": ["Jenny"],"Jenny": ["Jill", "Jeff"],
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"Jeff": ["James", "Jenny"]
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};
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```
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</section>
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